1. Field of the Invention
This invention relates to microwave spintronics and more particularly relates to an apparatus, system, and method for direct phase probing and mapping via spintronic Michelson inferometry.
2. Description of the Related Art
Microwave propagation in a dielectric medium underlies all responses of microwave energy interaction with the dielectric system. Therefore, it is generally accepted that the dielectric properties can be accurately reconstructed by characterizing the spatial distribution of absorbed microwave energy. Because the dielectric properties of the human body have significant differences between unhealthy and healthy tissues at microwave frequencies, microwaves are believed to have the capability for medical imaging and the pioneering works appear as early as 1986. Although much progress has been achieved in the past decade, microwaves are still considered to be a “potentially” powerful tool for medical imaging and far from clinical applications. One bottleneck here concerns the size of the detected object, since a curable tumor should have a size of a few millimeters, i.e., far shorter than the microwave wavelength (typical in a few 1 to 10 centimeters). Physically, such subwavelength features carried by the microwave field patterns contain spatial Fourier components with transverse propagation vectors kxy, larger than the wave vector k=ω√{square root over (∈μ)} in the media. This information may evanescently decays along z due to the imaginary number of kz=√{square root over (k2−kxy2)} and therefore is restricted to the near-field.
Another problem of microwave imaging relates to transmission line based approaches, where the sensitivity is limited by the background signal that comes from the transmission lines themselves. This parasitic noise significantly decreases the resolution of measurements. In addition, the antennas used in traditional microwave imaging, include a large amount of metallic materials, which may significantly distort the microwave propagation. Therefore a better data acquisition system with high sensitivity and an antenna compensation in the reconstruction algorithm is needed, which increases the burden of computation.
Spintronics, as a new discipline, has received much attention recently in an effort to upgrade electronic devices based on transport phenomena. From the dynamic point of view, spin dynamics have a much lower characteristic energy (μeV) in comparison with charge dynamics (meV-eV). Hence, spintronic devices may be applied for microwave applications. In contrast, conventional charge-dynamics-based electronics fit only to the infrared-optical regime. Advancement in microspintronics raises an intriguing question of whether a spintronic approach might transform microwave technologies, in a way similar to the case that microelectronics has revolutionized optical technologies.
As a cornerstone of coherent optics and spectroscopy, Michelson Interferometry as shown in FIG. 1(a) was developed from the ingenious Michelson-Morley experiment, where a sinusodial optical intensity I(Ψ)=|e1+e2eiΨ|2=|e1|2+|e2|2+2|e1·e2|cos Ψ was measured by modulating the electromagnetic phase Ψ. This enables probing Ψ which characterizes the phase of both the dynamic electric (e) and magnetic (h) fields.